scholarly journals Effect of an orientation-dependent non-linear grain fluidity on bulk directional enhancement factors

2021 ◽  
pp. 1-7
Author(s):  
Nicholas M. Rathmann ◽  
Christine S. Hvidberg ◽  
Aslak Grinsted ◽  
David A. Lilien ◽  
Dorthe Dahl-Jensen
Keyword(s):  
Basal Slip ◽  
Large Scale ◽  
Transversely Isotropic ◽  
Harmonic Series ◽  
Ice Flow ◽  
Flow Modelling ◽  
Bulk Strain ◽  
Enhancement Factors ◽  
Non Linear ◽  
Structure Tensors

Abstract Bulk directional enhancement factors are determined for axisymmetric (girdle and single-maximum) orientation fabrics using a transversely isotropic grain rheology with an orientation-dependent non-linear grain fluidity. Compared to grain fluidities that are simplified as orientation independent, we find that bulk strain-rate enhancements for intermediate-to-strong axisymmetric fabrics can be up to a factor of ten larger, assuming stress homogenization over the polycrystal scale. Our work thus extends previous results based on simple basal slip (Schmid) grain rheologies to the transversely isotropic rheology, which has implications for large-scale anisotropic ice-flow modelling that relies on a transversely isotropic grain rheology. In order to derive bulk enhancement factors for arbitrary evolving fabrics, we expand the c-axis distribution in terms of a spherical harmonic series, which allows the rheology-required structure tensors through order eight to easily be calculated and provides an alternative to current structure-tensor-based modelling.

scholarly journals Enhancement factors for grounded ice and ice shelves inferred from an anisotropic ice-flow model

2010 ◽  
Vol 56 (199) ◽  
pp. 805-812 ◽  
Author(s):  
Ying Ma ◽  
Olivier Gagliardini ◽  
Catherine Ritz ◽  
Fabien Gillet-Chaulet ◽  
Gaël Durand ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Actual State ◽  
Polar Ice ◽  
Ice Flow ◽  
Ice Shelves ◽  
State Of Stress ◽  
Asymptotic Models ◽  
Enhancement Factors ◽  
Definition Of ◽  
Stress And Strain Rate

AbstractPolar ice is known to be one of the most anisotropic natural materials. For a given fabric the polycrystal viscous response is strongly dependent on the actual state of stress and strain rate. Within an ice sheet, grounded-ice parts and ice shelves have completely different stress regimes, so one should expect completely different impacts of ice anisotropy on the flow. The aim of this work is to quantify, through the concept of enhancement factors, the influence of ice anisotropy on the flow of grounded ice and ice shelves. For this purpose, a full-Stokes anisotropic marine ice-sheet flowline model is used to compare isotropic and anisotropic diagnostic velocity fields on a fixed geometry. From these full-Stokes results, we propose a definition of enhancement factors for grounded ice and ice shelves, coherent with the asymptotic models used for these regions. We then estimate realistic values for the enhancement factors induced by ice anisotropy for grounded ice and ice shelves.

scholarly journals Oscillating non-linear large-scale structures in growing neutrino quintessence

2011 ◽  
Vol 418 (1) ◽  
pp. 214-229 ◽  
Author(s):  
Marco Baldi ◽  
Valeria Pettorino ◽  
Luca Amendola ◽  
Christof Wetterich
Keyword(s):  
Large Scale ◽  
Large Scale Structures ◽  
Non Linear ◽  
Scale Structures

scholarly journals Deformation in Rutford Ice Stream, West Antarctica: measuring shear-wave anisotropy from icequakes

2013 ◽  
Vol 54 (64) ◽  
pp. 105-114 ◽  
Author(s):  
S.R. Harland ◽  
J.-M. Kendall ◽  
G.W. Stuart ◽  
G.E. Lloyd ◽  
A.F. Baird ◽  
...  
Keyword(s):  
Shear Wave ◽  
Flow Direction ◽  
Transversely Isotropic ◽  
Shear Wave Splitting ◽  
Ice Crystal ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Wave Splitting

Abstract Ice streams provide major drainage pathways for the Antarctic ice sheet. The stress distribution and style of flow in such ice streams produce elastic and rheological anisotropy, which informs ice-flow modelling as to how ice masses respond to external changes such as global warming. Here we analyse elastic anisotropy in Rutford Ice Stream, West Antarctica, using observations of shear-wave splitting from three-component icequake seismograms to characterize ice deformation via crystal-preferred orientation. Over 110 high-quality measurements are made on 41 events recorded at five stations deployed temporarily near the ice-stream grounding line. To the best of our knowledge, this is the first well-documented observation of shear-wave splitting from Antarctic icequakes. The magnitude of the splitting ranges from 2 to 80 ms and suggests a maximum of 6% shear-wave splitting. The fast shear-wave polarization direction is roughly perpendicular to ice-flow direction. We consider three mechanisms for ice anisotropy: a cluster model (vertical transversely isotropic (VTI) model); a girdle model (horizontal transversely isotropic (HTI) model); and crack-induced anisotropy (HTI model). Based on the data, we can rule out a VTI mechanism as the sole cause of anisotropy – an HTI component is needed, which may be due to ice crystal a-axis alignment in the direction of flow or the alignment of cracks or ice films in the plane perpendicular to the flow direction. The results suggest a combination of mechanisms may be at play, which represent vertical variations in the symmetry of ice crystal anisotropy in an ice stream, as predicted by ice fabric models.

scholarly journals NON-LINEAR RESPONSE FUNCTIONS FOR TRANSVERSELY ISOTROPIC ELASTIC MEMBRANES/NETIESINĖS MEDŽIAGOS DARBĄ APIBŪDINANČIOS FUNKCIJOS SKERSAI IZOTROPINEI TAMPRIAI MEMBRANAI

2001 ◽  
Vol 7 (5) ◽  
pp. 345-351
Author(s):  
Rasa Kazakevičiūtė-Makovska
Keyword(s):  
Linear Response ◽  
Transversely Isotropic ◽  
Response Functions ◽  
Non Linear ◽  
Elastic Membranes

Membranai, pagamintai iš medžiagos, kurios fizinės savybės aprašomos deformacijos energijos funkcija W tūrio vienetui, deformacijos energijos funkcija Φ membranos vidurinio paviršiaus ploto vienetui gaunama integruojant funkciją W pagal membranos storį. (Nagrinėjama deformacijos energijos funkcija W neturi nustatytų apribojimų ir yra leidžiamos bet kokio dydžio deformacijos.) Funkcijos Φ tiksli išraiška yra išvesta skersai izotropinei medžiagai, kai izotropijos ašis sutampa su membranos nedeformuoto vidurinio paviršiaus normale. Parodoma, kad skersai izotropinei medžiagai gauta dvimatė membranos darbą apibūdinanti funkcija yra izotropinė ir išsamiai ištirta gautų fizinių priklausomybių struktūra. Tokios fizinės priklausomybės yra išvestos keturiems kontinuumo mechanikoje dažnai nagrinėjamų medžiagų tipams.

scholarly journals Large Scale Non-Linear Programming for PDE Constrained Optimization

2002 ◽  
Author(s):  
BART G VAN BLOEMEN WAANDERS ◽  
ROSCOE A BARTLETT ◽  
KEVIN R LONG ◽  
PAUL T BOGGS ◽  
ANDREW G SALINGER
Keyword(s):  
Linear Programming ◽  
Constrained Optimization ◽  
Large Scale ◽  
Pde Constrained Optimization ◽  
Non Linear Programming ◽  
Non Linear
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